Magnetic clutch



y 1952 J. A. CLARK ET AL 2,596,654

MAGNETIC CLUTCH Filed Feb. 15, 1949 2 SHEET SSHEET l INVENTORS. JAMES A.CLARK FRANK H. FERGUSON ATTORNEY y 13, 1952 J. A. CLARK ET AL 2,596,654

MAGNETIC CLUTCH Filed Feb. 15, 1949 2 SHEETS--SHEET 2 26 27 40 w 40 [5d/3 42 IO Fig. 4 Q E 5 I PS (3 E1 CONTROL CURRENT Fig. 5

Fig. 6

ATTORNEY Patented May 13, 1952 MAGNETIC CLUTCH James Atkins Clark,Takoma Park, and Frank Harvey Ferguson, Forestville, Md., assignors toAhrendt Instrument Company, Washington,

Application February 15, 1949, Serial No. 76,604

4 Claims. 1

This invention relates to magnetic connecting means for shafts.

Magnetic clutches and brakes are well-known in the art but have alimited use because of critical adjustments due to wear of parts.Furthermore, such clutches and brakes'have complicated structures andare impracticable for economical manufacture.

An object of the invention is the provision of a simple magnetic clutchwherein a driving shaft is coupled to an idle shaft by rotatable membersformed of magnetic materials and acting as bearings for the coordinatedends of the shafts when a magnetic flux is passed through the rotatablemembers.

Another object of the invention is the provision of a magnetic clutchwherein an idle shaft in longitudinal alignment with a driving shaft isconnected to the driving shaft by a plurality of rotatable bearings ofmagnetic materials when said bearings are attracted mutually upon theapplication of a magnetic flux, said bearings being confined incircumscribing relation on an abutting end of one of the shafts by acupshaped member rigid with one of the shafts, the magnetic flux beingcontrolled at will for varying the torque transmitted to the idle shaftfrom the driving shaft.

A further object of the invention is the provision of a clutch wherein adriving shaft and an idle shaft engage with positive but free-rollingcontact with needle bearings formed of magnetic materials, said bearingsbeing so aligned that the controllable magnetic flux of anelectromagnetic core will cause variations in the degree of frictionalsliding contact or binding between the needle bearings thereby varyingthe torque transmitted to the idle shaft.

Another object of the invention is the provision of a braking meanswherein a moving member has its speed of motion controlled by the actionof a magnetic flux on bearings formed of magnetic materials andcooperatively associated with the moving member and a stationary member,said bearings being freely rotatable during the absence of the magneticflux.

The invention is best understood from a consideration of the followingdetailed description in connection with the accompanying drawingsforming part, of the specification; nevertheless, it is to be; borne inmind that the invention is not confined to the disclosure but is suscep-'ferentially the free end 2| 2 features of the invention as expressed inthe appended claims.

These objects are attained by a mechanism, illustrated in theaccompanying drawings, in which Figure l is a longitudinal verticalsection of our magnetic clutch,

Figure 2 is a transverse vertical section taken along the line 22 ofFigure 1,

Figure 3 is a view in perspective and partly in section of a magneticclutch and an electric circuit therefor showing a slightly modifiedarrangement of the driving and driven shafts,

Figure 4 is a longitudinal vertical section showing another modifiedform of the clutch,

Figure 5 is a curve representing the torque transmitted from a drivingmember to a driven member as a function of control current in themagnetizing coil, and

Figure 6 is a longitudinal vertical section showing our clutch convertedinto a braking means.

Referring now particularly to Figures 1 and 2, ll] designates a drivingshaft which in turn may be rotated by any suitable prime mover (notshown). Spaced bearings II and I! support the driving shaft inlongitudinal axial alignment with a driven shaft 13 which transmitspower to an operating mechanism (not shown). Several specific examplesof such mechanisms may be a shaft for causing rotation of signal devicesor relays requiring quick response.

A thin cylindrical shell l5 has one end attached to an enlarged portionN5 of the driving shaft [0. The shell is manufactured from magneticmaterials and it will be noted from Figure 1 that it is in integralformation with the shaft I0. However, the shell may be formed separatelyfrom the shaft and firmly attached thereto in any approved manner. Theouter free end of shell or hollow portion of the driving shaft may havean inturned annular flange I1.

Rollers 20 which we designate particularly as needle bearings because ofthe small diameters, are received by the shell I 5 and embrace circumofthe shaft l3. Lubricant is supplied in any approved manner to the rollerbearings which may serve normally as bearing supports for the drivenmember. The bearings, due to the fact that they are manufactured frommagnetic materials, and

have relatively small circumferential clearance .-.:between rollers playan important part in the tible of such changes and modifications asshall v define no material departure from'tlie salient functioning ofthe magnetic clutch. The thickness of the walls of the hollow portion I5of the shaft IO may also be a contributing factor in the efficientoperation of the clutch. The small clearance is substantially the sameas is found in well-constructed roller bearings of standard makes, withthe rollers for all practical purposes, being in contact with each otherand also being in contact with the shell (5 and shaft [3.

An electromagnet generally designated by the numeral (Figures 1 to 3)includes the usual north pole 26, a south pole 21 and a magnetic coil28. The ends of the poles are curved to conform to the curvature of theshell, cup or hollow portion l5 of the shaft [0 with the curved surfacesof the poles being in close association with the outer surface of saidshell to form an air gap.

The electric circuit in which is embodied the magnetic coil 28, includesa wire 29 connecting a source of current 30 with one end of said coiland an arm 3|, movable over a resistance 32. This resistance, which inturn is connected to the other end of the coil by a wire 33, isconnected with the source of current by a wire 34 and the arm 31.

The shell may be attached to the shaft 13a (Figure 3) for confining thebearings 20 in circumscribed relation on the free end of the shaft lila.In other words, it is immaterial, for the purposes of this constructionwhether the shaft [0 or HJa be the driving or driven shaft or whetherthe shell is rigid with the shaft In or Ilia or the shaft l3 or l3a.

An alternative form whereby the thin wall construction illustrated inFigure 1 may be avoided,

is shown in Figure 4 wherein the hollow portion l5a of the shaft I0 isformed of alternate rings of magnetic material and ring 4| ofnonmagnetic material so that a magnetic shunt is not offered to theflux. In addition, the adjacent ends 42 of alternate rollers 43 havebeen reduced in diameter while the ends 44a of the other rollers 44 arealso reduced so that the flux passing from the north pole piece 26 tothe south pole piece 21 must pass between adjacent rollers 43 and 44thereby tending to bind the rollers to each other more thoroughly. Morespecifically, the air gap created by the reduced ends 42 and 44a of therespective rollers 43 and 44 will cause the flux to pass from the pole26 through a ring 40 and through the non-reduced ends of the rollers 44thence to the adjacent rollers 43 through a ring 40 and to the pole 2!through the non-reduced ends of the rollers 43. Thus, the lines of forceof the magnetic field take the paths of least reluctance. The rings 40and 4! are pressed onto each other with one of the rings 40 beingpressed onto the member l5 so that said rings will revolve with theshaft [0.

The operation of the magnetic clutch is as follows. The shaft i9 may beconsidered the drivin shaft which is rotated by a prime mover (notshown) while the shaft 13 is idle but adapted to operate any type ofmechanism when the transmission is active. When the electric circuit(Figure 3) is closed by the proper position of the arm 3|, the magneticflux will flow through the shell [5 and cause the rolling members 20 tobind the shell l5 to the end 2| of the shaft. It has been found inactual practice that the best results have been obtained when themagnetic flux is passed through the shell, the bearings, and shaft endsurrounded by said bearings so that the bearings will not only beattracted to each other but will be attracted to the cupand shaft end.

It is understood that the degree of binding is dependent upon themagnetic intensity which increases in proportion with the current. Themagnetic intensity is therefore determined by the adjustable resistance32 which controls the current to the magnetic coil 28. Thus, as thecurrent is decreased sufficiently there will be slippage in the clutchelements and the torque transmitted will be decreased.

Figure 5 illustrates diagrammatically the variation in transmittedtorque between the shell l5 and shaft end 2| as a function of thecontrolled current. The shape of this curve as is wellknown, may bealtered by the selection of various magnetic constructions and by theproperties of the magnetic materials employed in the transmission aswell as in constructional features thereby eliminating an air gap by theuse of a rotatable core and coil supplied with current by means of sliprings and collector brushes.

It will be seen from the above description that the magnetictransmission is simply constructed and does not require any additionalmedium or element to initiate the binding of the rollers. In otherwords, the conventional rolling members 2!! having a uniform shape andsize and housed within a casing 15 rigid with a driving or driven shaft,form bearings for the free end of a second shaft with means, such as anelectromagnet or a permanent magnet, for passin a magnetic flux throughthe casing, bearings and the free end of the second shaft.

In Figure 6 is illustrated broadly, one form of a magneticallycontrolled braking means which is a simple conversion of the magneticclutch illustrated in Figure 3. In this form shaft 45 is driven whileshaft 45 is held stationary as is the cupshaped member 41 which is rigidwith the shaft 46. The last-mentioned shaft may be keyed to a stationarybracket 48 as shown at 49 or some other form of clamping means may beemployed. The member 41 confines the bearings 50 to the free end of theshaft 45. On the other hand the cup-shaped member 4! may be rigid withthe shaft 45 as shown in Figure l. The magnet as will be appreciated,may be held stationary and the bearing surfaces of the member 41 may beintegral with the pole pieces.

The operation of the braking device is identical with that of theclutches described supra. When a magnetic flux is caused to flow throughthe bearings 50 by the magnet 5|, the speed of the shaft 45 will bedecreased in accordance with current passing through the coils of themagnet. In other words the shaft may be stopped or the speed may beprogressively decreased, at will.

The casing, cup-shaped member, or cylindrical enlargement employed inall of the constructions and rigid with one of the pair oflongitudinally aligned shafts which may be a driving or driven or astationary element, is adapted to confine the roller bearings, onto theother element. Said bearings create a frictional drag between the pairof elements when a magnetic flux is passed through the bearings.

What is claimed:

1. In a device of the class described, a member, a second memberassociated in longitudinal axial alignment with the first member, one ofsaid members constituting a driven element, a casing rigid with one ofthe members and embracing a portion of the other member, roller bearingsin contact witheach other formed of magnetic material and confined bythe casing on the embraced portion of said other-member, and meanspassingamagneticfiux'through the bearings to cause said hearings tocreate a frictional drag between the members, the portions of saidmembers em bracing the roller bearings being made of magnetic materialsand in contact with said bearings.

2. A magnetic clutch comprising a pair of longitudinally aligned shaftsformed of magnetic materials, an end of one shaft received within anadjacent end of the other shaft, free-rolling bearings arranged in asingle circumferential row, confined in contact with the bearingsurfaces of the associated ends of the shafts and formed of magneticmaterials, the roller bearings being in contact with each other and incontact with the shaft ends, an end of each of alternate bearings and anoppositely disposed end of each of the other bearings being reduced indiameter, and means causing a magnetic flux to flow through thebearings, the reduced ends of the bearings providing air gaps at saidends so that the flux will pass through adjacently disposed bearings.

3. A magnetic clutch comprising a pair of shafts in longitudinal axialalignment, a conventional roller bearing including roller bearings and acasing fixed to an end of one of the shafts for the reception of thefree end of the other shaft and for confining the rollers of thebearings circumferentially around the enclosed end of the secondmentioned shaft, the shaft ends, as well as the roller bearings beingformed of magnetic materials, and means causing a magnetic flux to passthrough the roller bearing, said bearings being formed of magneticmaterials to cause a frictional drag between the shafts, the rollerbearings being substantially in contact with each other and in contactwith the shaft ends.

4. A magnetic clutch comprising a pair of longitudinally alined shaftsformed of magnetic materials, a free end of one shaft being hollow andreceiving an adjacent free end of the other shaft, free-rolling membersdisposed in substantial contact with each other between the bearingsurfaces of the associated ends of the shafts, each rolling member beingsubstantially in contact at diametrically opposite points with saidbearing surfaces of the shaft ends and formed of magnetic materials, thehollow end of the first mentioned shaft cooperating with the rollingmembers to act as bearings for the adjacent end of the other shaft andto form the sole support for said end, and means causing a magnetic fluxto be passed through the rolling members and the adjacent shaft ends tocreate a frictional drag between the shafts.

JAMES ATKINS CLARK. FRANK HARVEY FERGUSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,300,223 Hottenroth, Jr Oct.2'7, 1942 2,417,850 Winslow Mar. 25, 1947 OTHER REFERENCES "NationalBureau of Standards Technical Report 1213, Apr. 1948.

